The generation of monoclonal antibodies against human proteins is a central component of molecular diagnostics and the development of protein based assays for human molecular medicine. Likewise, in some settings, monoclonal antibodies are highly efficacious therapeutic modalities. In both diagnostics and therapeutics, fine specificity of the antibody is often required. In some cases, such as blood typing and transfusion medicine, the antibodies are not useful unless they recognize the target epitope on the surface of an intact cell. For the vast majority of blood group antigens, the epitope of interest consists of a single amino acid polymorphism in an exofacial domain of the protein in question. In the United States alone, approximately 14 million units of red blood cells (RBCs) are transfused per year. Besides the well known ABO and RhD blood group antigens, several hundred additional antigens have been described, which vary widely throughout the genetically divergent human population. Thus, each transfusion recipient has the potential to make an antibody response against a wide array of foreign antigens. Once an antibody is made, it is often unsafe to transfuse additional RBCs that express the antigen; as such cells are lysed when recipient antibodies bind to them. The negative effects of this are not limited to a loss of the potential therapeutic effects of the transfused RBCs; indeed, the lysis of transfused RBCs can lead to renal failure, shock, disseminated intravascular coagulation, and in some cases death. It is for this reason that every transfusion recipient undergoes a screen for antibodies against RBC antigens prior to being transfused. In the event that an antibody is detected, its antigenic specificity is identified. The patient is then only transfused with RBCs that do not express antigens recognized by the recipient antibodies. Thus, potentially fatal hemolytic transfusion reactions are avoided.
In order to identify antigen-negative units of RBCs for patients who have developed an alloantibody, one must be able to phenotypically characterize antigens on the surface of donor RBCs. This is accomplished by incubating RBCs with antibodies specific for the antigen in question, under conditions that induce RBC agglutination, when the antibody recognizes the RBCs. Thus, to phenotypically characterize antigens on the surface of RBCs, one must have an extensive panel of antibody reagents, each of which recognizes a different relevant blood group antigen. Traditionally, such antibodies were acquired from antiserum of patients, who had previously become alloimmunized by a transfusion, and now served as donors to generate the antibody reagents. However, there are several problems in using human alloimmunized donors as the source for RBC typing antibodies, including: 1) Logistical problems of maintaining a consistent schedule of donation, 2) limited supply of serum given a donor safety concerns regarding frequency of donation, 3) questions of specificity as additional antibodies may also be present, 4) inconsistence of the reagents from donor to donor, and 5) changing of the nature of the antisera in a given donor as a function of time (changing titers, affinity maturation, etc.). It is for these reasons that monoclonal antibodies are highly desirable and superior as typing reagents. However, manufacture of human monoclonal antibodies can be very difficult; therefore, a number of human blood group antigens still do not have monoclonal antibodies that can recognize them (e.g. Duffy A, Duffy B, S antigen, etc.), and new approaches for detecting single amino acid polymorphisms as well as generating antibodies that are capable of detecting single amino acid polymorphisms are needed.